3. Selection parameters and allowable values of copper tubes for refrigerant piping
The selection of copper tubes for refrigerant piping needs to consider many factors, including the size, type, wall thickness and working pressure of the copper tube. For example, the ASTM B280 standard specifies the size and working pressure of copper tubes in the field of air conditioning and refrigeration. The selection of copper tubes should meet the specific requirements of the refrigeration system, including the type of refrigerant, system capacity and design pressure.
1. Chinese standards:
National standards such as GB/T 17791-2017 provide detailed guidance for the selection of copper tubes for refrigerant piping. These standards include specific requirements for the copper tube sizes required for different types of refrigerant systems (such as R22, R410A, R32, etc.), as well as the maximum allowable working pressure and temperature.
By combining specific engineering requirements with applicable Chinese national standards, it can be ensured that the selection of copper tubes meets the performance and safety requirements of the system. For example, the standard may indicate how to select the appropriate copper tube size and wall thickness according to the refrigerant type and system design under certain working conditions, and how to ensure that these parameters operate within a safe range.
2. European standards:
In Europe, copper pipes and tubes are classified as "Type X Copper Pipe", "Type Y Copper Pipe", and "Type Z Copper Pipe" according to the EN 1057 standard; in Australia, they are classified as "Type A", "Type B", "Type C", and "Type D".
These different types of copper pipes are divided into soft copper pipes and hard copper pipes according to their stiffness. Soft copper pipes are more expensive due to annealing heat treatment, but are easy to install and maintain, and are suitable for occasions that require delicate wiring, such as domestic water supply pipes or HVAC systems. Hard copper pipes have thicker walls and can withstand higher pressures and temperatures. They are usually used for main water supply pipes, gas pipes, and industrial applications.
3. Selection parameters and allowable values of copper pipes for general refrigerant piping
O and OL materials (TP2M type, also known as coils in engineering)
1/2H or H material (TP2 type, also known as straight pipes in engineering)
Fourth, what are the problems in the use of air conditioning copper pipes? How to solve them?
1. Copper tube leakage:
Copper tube leakage is a fatal defect of air conditioners. Once leaked, the refrigerant of the air conditioner will overflow, and the air conditioner will fail due to lack of heat transfer medium. The reasons for copper tube leakage are relatively complicated. The following are the common reasons for leakage.
(1) Manufacturing reasons:
① Eddy current flaw detection missed. GB stipulates that copper tubes must be 100% eddy current flaw detection, and stipulates the diameter of artificial defects (through holes) on the sample tube used to calibrate the flaw detector to ensure the sensitivity of eddy current flaw detection and prevent excessive defects from being missed. This requirement can be fully guaranteed in regular large copper tube factories, because flaw detection is online detection. This online eddy current flaw detection ensures that all lengths of the tube are eddy current tested, which is 100% flaw detection. Some copper tube factories are not like this, or do not perform eddy current flaw detection, or use low-standard eddy current flaw detectors for random inspection. In this way, the copper tube has defects that exceed the standard and are missed or not detected, causing the air conditioner to leak when the user uses it;
② The eddy current flaw detection detects defects, but the copper tube surface is not marked or the marking is inaccurate or unclear. In the production process of copper tubes, the defects detected by eddy current flaw detection require to be covered with ink on the defects that exceed the standard, so that the user can remove the defective copper tube during use. However, due to the insufficient adhesion of the ink selected by the manufacturer during the production process, the improper adjustment of the inkjet gun, the incomplete drying, and the fading of the ink components when exposed to high temperature, the user cannot pick out the defects detected by eddy current flaw detection during use. Once the defective copper tube is used in the air conditioner, it will inevitably cause leakage.
(2) Reasons for user use:
① Misuse of defective tubes detected by eddy current flaw detection. Under normal copper tube production conditions, copper tube eddy current flaw detection not only marks the number of damage points on each coil, but also paints the damage point with black marks so that users can identify and pick out this "black tube" during use. Air conditioning and refrigeration companies should explain this clearly to operators, especially new workers, in order to prevent such damaged pipes from being installed on air conditioning and refrigeration devices. We have found this problem many times when we go deep into user services. Some workers asked us what happened to the black color on the pipe, and some dissected unqualified products and found that it was precisely because the "black pipe" was installed on the product that caused the air conditioning and refrigeration device to leak.
② Processing problems. In the process of forming two devices, the air conditioning main pipe must go through the links of bending, expanding, expanding, and welding.
③ Leakage caused by poor welding. After the copper pipe is inserted into the perforated aluminum foil, the pipes must be connected, and a small elbow is needed to connect them. In order to make the connection firm, during the production process, the small elbow is welded to the copper pipe with solder. The welding method is divided into manual and automatic. During welding, due to the quality of solder, the expansion of the copper pipe, and foreign matter on the welding surface, the welding is not solid, forming a virtual weld, causing refrigerant leakage.
2. Cracks in copper pipes:
The cracks in copper pipes are mainly concentrated in the expansion and expansion processes of copper pipes. The cracking situation is shown in Figure 1. In the production of the two devices, the expansion and expansion of copper tubes is a continuous process, which is often completed in one process. There are many reasons for the cracking of copper tubes, and the main reasons are as follows:
① The quality of the copper tube itself. The reasons for the quality of the copper tube itself can be divided into external surface defects, internal surface scratches, and internal surface oxidation. During the cold processing deformation of the copper tube during expansion and expansion, the surface is elongated by tensile stress. When there are deep scratches on the outer surface of the copper tube, the outer surface of the copper tube cannot withstand the surface tensile stress, resulting in a pull-off phenomenon, which is the cracking of the outer surface of the copper tube we see. The cracking mechanism caused by scratches on the inner surface of the copper tube is similar to the cracking mechanism caused by scratches on the outer surface. When the inner surface of the copper tube is oxidized, the friction force on the inner surface of the oxidized copper tube is different from that on the inner surface of the unoxidized copper tube during expansion, resulting in inconsistent lengths of the lower piers of copper tubes of the same length. When expanding, the copper tube with a small amount of lower piers extends a long length, resulting in excessive expansion and cracking.
Figure 1: Partial cracking of air conditioner copper tubes
② Reasons for user use. When copper tubes are used, they are often straightened and cut to size. Cutting is usually done by chipless cutting. The surface of copper tubes is relatively soft after heat treatment. When cutting without chips, if the cutter is unfavorable or the cutter is too large, the copper tube will shrink too much or have too many burrs, forming port flash and port hardening, which will cause cracking when expanding. A heat exchanger is composed of many "U"-shaped tubes. The consistency requirements of the length of each "U"-shaped tube and the length of the two ends of each "U"-shaped tube are very high. When bending the "U"-shaped tube, due to equipment or adjustment, the length of each "U"-shaped tube and the length of the two ends of each "U"-shaped tube are too different (greater than 2mm). Therefore, when expanding, the port will be too long and the copper tube will extend too long, causing the expansion to be too large and cracking.
3. Wrinkling and fracture of bent tubes:
Wrinkling and fracture of copper tubes (Figure 2, Figure 3) occur in the process of making "U"-shaped tubes. Copper tubes are often scrapped in this process.
